A suspension damper, commonly referred to as a shock absorber, reduces the amplitude of resilient suspension excursions between a sprung mass and an unsprung mass of a motor vehicle by converting into work a fraction of the kinetic energy of the sprung mass. Typically, a suspension damper includes a fluid-filled cylinder tube connected to the unsprung mass, a piston in the cylinder tube connected by a rod to the sprung mass, and valves on the piston which throttle fluid flow across the piston during compression and rebound strokes of the suspension damper attributable to relative suspension excursions between the sprung and unsprung masses. An example of a suspension damper is set forth in U.S. Pat. No. 6,161,662, the disclosure of which is hereby incorporated by reference. In a twin-tube suspension damper, fluid in the cylinder tube displaced by the connecting rod during a compression stroke of the suspension damper flows through a base valve to an annular reservoir around the cylinder tube and returns through the base valve during a rebound stroke of the suspension damper. In a monotube suspension damper, the volume of a gas chamber at an end of the cylinder tube opposite the connecting rod decreases and increases, respectively, during compression and rebound strokes of the suspension damper as the connecting rod enters and withdraws from the cylinder tube.
Suspension dampers are typically attached to a spring assembly of a vehicle suspension system. The spring force generally determines the height of the vehicle, and the damper controls the dynamic vehicle motion. Often, it is desirable to supplement the spring force to maintain a controlled vehicle height at different levels of vehicle load. One method of doing so is to affix a height leveling damper to the suspension system that adjusts the height of the vehicle relative to the load on the vehicle. To maintain the controlled vehicle height, the spring force may be supplemented with an air leveling damper that requires an external compressor and controller. An air sleeve is attached to the outside of the air leveling damper to supply an extending force to the damper for maintaining the controlled vehicle height. An example of a height leveling damper is set forth in U.S. Pat. No. 6,382,371, the disclosure of which is hereby incorporated by reference.